When to plant sweet alyssum in Sacramento, California
December 29 – January 5
Transplant outdoors · typical Sacramento yearClimate basis: NOAA station Sacramento 5 Ese, CA (USW00023271), 5 mi (7 km) from downtown Sacramento (ZCTA 95814 centroid), elevation 38 ft, on the 1991–2020 climate normals. Transplant sweet alyssum outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (January 12). One year in ten still freezes after February 8.
The Sacramento year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to Feb 8
Every method, with its sources
Start seeds indoors
Dec 1 – Dec 15Colorado State's seed-starting table lists sweet alyssum (Lobularia) at 6 weeks before the average frost-free date in the 'Indoors' column, the only indoor figure found that is anchored to frost rather than to the outdoor planting date, so indoor sowing opens 6 weeks before the median last freeze. Anchored to the median last spring freeze (Jan 12). Colorado State University Extension
Transplant outdoors
Dec 29 – Jan 5Wisconsin Horticulture puts hardened-off transplants in the garden a week or two before the average last frost, which starts later than Illinois' four-weeks-before hardy-annual rule, so the more frost-conservative Wisconsin interval governs. Anchored to the median last spring freeze (Jan 12). University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture) · Clemson Cooperative Extension Home & Garden Information Center · Colorado State University Extension · University of Illinois Extension · Clemson Cooperative Extension Home & Garden Information Center
Direct-sow outdoors
Dec 15 – Dec 29Illinois Extension names sweet alyssum in its hardy-annual list and quantifies those at about four weeks before the frost-free date, and Clemson corroborates the direction by saying seed should be directly sown several weeks before the last frost date, so direct sowing opens 4 weeks before the median last freeze. Anchored to the median last spring freeze (Jan 12). Clemson Cooperative Extension Home & Garden Information Center · Clemson Cooperative Extension Home & Garden Information Center
Variety assumption: Assumes seed-grown Lobularia maritima, which Clemson notes flowers within 6 to 8 weeks of sowing and may stop blooming as summer heat rises; sources disagree on hardiness — Illinois and NC State call it a hardy annual while Clemson lists it as half-hardy, so the more cautious semi-hardy class is used.
These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.
Crop rule sources (5)
- Colorado State University Extension: Growing Annual Plants from Seed (accessed 2026-07-25)"Table 1: Starting times for seeds grown indoors and in cold frames, shown as number of weeks to start seed before average frost-free date."
- Clemson Cooperative Extension Home & Garden Information Center: Sweet Alyssum (accessed 2026-07-25)"Sweet alyssum can easily be grown from seed and should be directly sown in the garden several weeks before the last frost date in spring."
- Clemson Cooperative Extension Home & Garden Information Center: Growing Annuals (accessed 2026-07-25)"Half-hardy annuals – such as allysum and dianthus -can tolerate light frost and are usually planted in early spring for spring and early summer color."
- University of Wisconsin-Madison Division of Extension (Wisconsin Horticulture): Sweet Alyssum, Lobularia maritima (accessed 2026-07-25)"Transplants that have been hardened off can be placed in the garden a week or two before the average last frost, otherwise tender transplants should be protected until add danger of frost is past."
- University of Illinois Extension: Annuals — Flowers (accessed 2026-07-25)"Ornamental cabbage and kale, pansy, snapdragon, sweet alyssum, calendula and dusty miller"